Milk is a perishable product, the quality of which is dependent on a number of parameters. One of the most significant parameters affecting the quality of milk is temperature.
During the milking process, milk leaves the cow at approximately 37.degree. C. As the milk passes through the milking machine it loses heat. The milk also passes through a water chiller or heat exchanger which chills the milk down to approximately 18.degree. C. before the milk enters a milk vat. The milk vat is also refrigerated to cool the milk down even further.
The growth of bacteria in the milk is directly affected by the temperature of the milk. Bacterial growth is exponential. The longer the milk stays at a high temperature, the greater the bacterial growth and thus the more adverse the quality of the milk.
When the milk is collected by a tanker from the milk vat, the temperature of the milk is recorded to give an indication if the milk vat is cooling the milk appropriately or to act as a indicator if samples of the milk taken test high for bacterial growth.
While the temperature of the milk as it leaves the vat gives an indication as to the possible quality of the milk, this is not an accurate indication as the milk may have been sitting a high temperature for a period of time before collection.
One poor quality batch of milk can contaminate other milk held in the tanker. Thus, a whole tanker full of milk can be wasted. Alternatively, poor quality milk is used in less profitable products such as casein instead of milk powder.
Thus, it is possible for literally millions of dollars per annum to be wasted through the inadvertent contamination of milk or low quality milk in general.
These problems have been recognised internationally. Previously the temperature of milk at the time of tanker collection was recommended to be in the order of 7.degree. C. It is now likely that there may be a ruling that requires milk temperatures to be only 5.degree. C. at the time of tanker collection.
This ruling may be difficult to effect. This is because the temperature of milk entering the milk vat after exiting the chiller system heat exchanger may be in the range of 14-20.degree. C. The current deadline requires the temperature to be reduced to 7.degree. C. within the three hour period. It may also be a requirement that milk is chilled to 5.degree. C. in the three hour period, however there is presently no means of monitoring this.
Without accurate information as to whether the requirements for milk temperature are met, it is difficult for dairy factories to make appropriate operational decisions. Traditionally these decisions have been made on factors such as history, local knowledge, averaging, weather allowances and guess work.
This is further complicated by the seasonal trends in the dairy industry. For commencement of the season there is gradual increase to the peak or flush period of the dairy season. This flush period may last for approximately 10 days and the downward trend begins, ongoing until the season ends.
Understandably all these variations can lead to costly mistakes made in operational procedures as there is little data on which to base decisions or predictions.
A number of devices have been developed to combat the problems associated with retaining milk in a vat over time.
Once such device is described in WO 94/16552, Maasland. The device described in this specification is used to automatically activate a milk vat cooler once a specific level of milk is contained in the vat. Milk level sensors are positioned inside the vat to give an indication of the amount of milk contained, and to activate the cooling device. The device also logs temperature measurements for each animal's milk which is added to the vat.
However, this device cannot provide any indication of the quality of milk stored within the vat. The device only allows automatic activation of a milk vat's cooler mechanism depending on the amount of milk retained in the vat.
Another related device is described in U.S. Pat. No. 4,612,537, Meltais. The device described in this specification is a warning device which includes temperature sensors in a milk vat. The temperature sensors are used to determine the temperature of milk contained within the vat, and trigger an alarm signal if the milk temperature in the vat rises above a pre-determined value.
However, the device described in this specification cannot provide any indication of the equality of milk stored within the milk vat. This device may only give a warning when the milk temperature exceeds a certain threshold value.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the following description which is given by way of example only.